Near-field optical storage medium and optical data storage system therefor

ABSTRACT

An optical data storage system writes or reads information with respect to an optical storage medium using an optical pickup including a solid immersion optical system or a solid immersion lens for generating a near-field and emitting a light beam. The optical storage medium includes a recording layer which is formed on a surface of an optical transmissive layer opposite to another surface of the optical transmissive layer which opposes the solid immersion optical system or solid immersion lens. The thickness of the optical transmissive layer is larger than one wavelength of the light beam. The interval between the surfaces of the solid immersion lens or solid immersion optical system and the optical transmissive layer is smaller than one wavelength of the light beam. Thus, the light beam reflected from the inside of an air gap and the inside of the optical storage medium between the air gap and the recording layer does not function as noise with respect to the light reflected from the recording layer. Also, since the thickness of a protective layer or a substrate which is an external surface of the optical storage medium can be thickened, information can be written or read with respect to the optical storage medium even when the optical storage medium has dust and/or damage.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.10/151,908, now allowed, which is a divisional application of U.S.application Ser. No. 09/301,607, now U.S. Pat. No. 6,621,787, whichclaims the benefit of Korean Application Nos. 98-38738, filed Sep. 18,1998 and 99-5043, filed Feb. 12, 1999, in the Korean Patent Office andU.S. Provisional Patent Application No. 60/100,778, filed Sep. 18, 1998,the disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a near-field optical storagemedium and an optical data storage system having a focusing opticalsystem, and more particularly, to an optical storage medium which isused together with an optical pickup having a near-field focusingoptical system such as a solid immersion optical system or a solidimmersion lens, and a near-field optical data storage system forperforming writing and/or reading of information with respect to theoptical storage medium.

[0004] 2. Description of the Related Art

[0005] In an optical data storage system, an optical pickup having asolid immersion optical system or solid immersion lens performs writingand/or reading of information with respect to the optical data storagemedium, using a near-field formed between the solid immersion opticalsystem or solid immersion lens and the optical data storage medium.

[0006]FIGS. 1 and 2 show an existing optical disc used as an opticaldata storage medium, in which FIG. 1 shows that an existing optical discis used together with the optical data storage system having acatadioptric solid immersion optical system, and FIG. 2 shows that anexisting optical disc is used together with an optical data storagesystem having a refractive type solid immersion lens.

[0007] In FIG. 1, a light beam 1 emitted from a light transmission andreception portion 10 is reflected by a reflective mirror 12 and incidentto a catadioptric solid immersion optical system 14. A slider 16supporting the solid immersion optical system 14 aerodynamically raisesthe solid immersion optical system 14 aerodynamically through an airbearing generated by a relative movement between an optical storagemedium 18 such as an optical disc and the slider 16. As a result, an airgap is formed between the solid immersion optical system 14 and aprotective layer 183 of the optical storage medium 18. An interval ofthe air gap, that is, a distance between the opposing surfaces of thesolid immersion optical system 14 and the optical storage medium 18, ismaintained for example within one wavelength of light used. It ispreferable that it is maintained much smaller than one wavelength of theused light. The catadioptric solid immersion optical system 14 refractsand reflects the light beam 1 incident from the reflective mirror 12,and forms a beam spot focused on its surface opposing the opticalstorage medium 18. The beam spot forms a near field in the air gapbetween the solid immersion optical system 14 and the surface of theoptical storage medium 18.

[0008] The optical data storage system shown in FIG. 2 includes afocusing objective lens 24 and a refractive solid immersion lens 26,instead of the catadioptric solid immersion optical system 14 shown inFIG. 1. A light transmission and reception portion 20 emits a light beam1 having an optimized diameter for the objective lens 24. A reflectivemirror 22 reflects the light beam 1 emitted from the light transmissionand reception portion 20 toward the objective lens 24. The objectivelens 24 focuses the light beam 1 incident from the reflective mirror 22on the solid immersion lens 26. The beam spot focused on the solidimmersion lens 26 forms a near field between a surface of the solidimmersion lens 26 opposing the optical storage medium 18 and aprotective layer 183 in the optical storage medium 18. The objectivelens 24 and the solid immersion lens 26 are supported by a slider 28.Like the slider 16 shown in FIG. 1, the slider 28 aerodynamically raisesthe solid immersion lens 26 and forms an air gap having an intervalwithin one wavelength of light used between the solid immersion lens 26and the optical storage medium 18.

[0009] In the optical data storage system shown in FIG. 1 or 2, a beamspot is formed in a near field generating portion being a predeterminedposition on the surface of the solid immersion optical system 14 or thesolid immersion lens 26 which opposes the optical storage medium 18. Ingeneral, the system shown in FIG. 1 or 2 uses a fine beam spotcorresponding to a numerical aperture (NA) of at least one for writingor reading information with respect to the optical storage medium 18. Inthe case that the used light has a wavelength λ of 650 nm, a light beamwhich forms a beam spot on the near field generating portion passes anair gap of an interval of approximately 110 nm and a protective layer183 of 70-90 nm thick, and is transferred to a recording layer of theoptical storage medium 18. The recording layer is disposed between theprotective layer 183 and a substrate 181 of the optical storage medium18. The light beam reflected from the recording layer transmits throughthe protective layer 183 and the air gap and is transferred to the solidimmersion optical system 14 or the solid immersion lens 26.

[0010] Generally, according to the refraction and total reflection laws,the light contributed to a large numerical aperture is totally reflectedfrom the emergence surface of the solid immersion optical system 14 orthe solid immersion lens 26, that is, the near field generating portionbeing an optical transmitting surface adjacent to the optical storagemedium 18. Therefore, in the case that the interval of the air gap islarger than the wavelength λ of the used light, the optical storagemedium 18 is positioned in the portion beyond the near field. Thus, thelight contributed to the large numerical aperture does not contribute toformation of the beam spot on the optical storage medium 18. In otherwords, the numerical aperture of the light beam contributed to theformation of the beam spot on the optical storage medium 18 becomessmaller than “1”, while passing through the air gap. As a result, a spotsize of the light beam focused on the optical storage medium 18 with thelight traveling through the air gap having an interval larger than thewavelength of the used light, becomes larger than a size of the beamspot formed on the near field generating portion of the solid immersionoptical system 14 or the solid immersion lens 26. However, in the casethat an interval of the air gap is sufficiently smaller than onewavelength of the used light, preferably λ/4, the spot size of the lightbeam incident to the optical storage medium 18 is close to the size ofthe beam spot formed in the near field generating portion. Therefore,under this condition, the optical data storage system shown in FIG. 1 or2 can write or read information at high density with respect to therecording layer of the optical storage medium 18, using the solidimmersion optical system 14 or the solid immersion lens 26.

[0011]FIG. 3 shows the near field generating portion between the surfaceof the solid immersion optical system 14 or the solid immersion lens 26and the protective layer 183 of the optical storage medium 18. Theinterval SRD from the surface of the solid immersion optical system 14or the solid immersion lens 26 opposing the optical storage medium 18 tothe protective layer 183, more accurately, to the recording layer,becomes smaller than one wavelength of the used light, and the recordinglayer in the optical storage medium 18 is positioned within the distanceproviding a near field effect.

[0012] An example of an existing optical disc is disclosed in U.S. Pat.No. 5,470,627. In the case that the above existing optical disc is forexample a magnetooptical disc, the disc includes a reflective layer, afirst dielectric layer, a recording layer, and a second dielectric layerwhich are disposed on a conventional substrate in sequence. Thereflective layer is made of metal such as an aluminum alloy having a500-1000 Å thickness. The first dielectric layer is made of aluminumnitride or silicon nitride having a 150-400 Å thickness. The recordinglayer is made of rare-earth transition-metal alloy such as TbFeCo havinga 150-500 Å thickness. Finally, the protective layer is made of siliconnitride Si₃N₄ having a 400-800 Å thickness.

[0013] However, in the case that the above-described existing opticaldisc is used, the optical data storage system has two problems asfollows. These problems take place identically in both the data storagesystem including the solid immersion optical system 14 and the datastorage system including the solid immersion lens 26. Therefore, forconvenience of explanation, these problems will be described inconnection with the existing optical disc and the solid immersion lens26.

[0014] First, the problem that the light beam reflected from therecording layer of the existing optical disc having the above structurecontains noise due to interference will be described with reference toFIGS. 4 and 5. FIG. 4 shows the solid immersion lens 26 having arefractive index of 1.8. In FIG. 4, “air gap reflective light (NB)”illustrates the light beam totally reflected from the near fieldgenerating portion of the solid immersion lens 26 and the air gapbetween the solid immersion lens 26 and the optical storage medium 18,and “recording layer reflective light (RB)” illustrates the light beamreflected from the recording layer in the optical storage medium 18. Inthe case that the solid immersion lens 26 has a refractive index of 1.8,the total reflective angle of 56.3 degree at the solid immersion lens 26corresponds to the numerical aperture of 0.83. FIG. 5 showsangle-reflectance characteristics of the solid immersion optical system14 or the solid immersion lens 26 with respect to three air gapintervals. In FIG. 5, curves (a) show angle-reflectance characteristicswith respect to the air gap interval of 50 nm, curves (b) showangle-reflectance characteristics with respect to the air gap intervalof 100 nm, and curves (c) show angle-reflectance characteristics withrespect to the air gap interval of 150 nm. Among the curves (a) through(c), the curves denoted as “++” show angle-reflectance characteristicswith respect to the p-polarized light beam, and the curves denoted assolid lines show angle-reflectance characteristics with respect to thes-polarized light beam. The angle denoted at the horizontal axisindicates an incident angle possessed by the light beam proceeding tothe air gap from the solid immersion lens 26. For example, in the casethat an interval of the air gap existing between the optical storagemedium 18 and the solid immersion lens 26 becomes larger than thewavelength of the used light, the portion of the light beam having anangle larger than the total reflection angle of 56.3 degree,particularly the portion of the light beam contributed to a highernumerical aperture, for example, the numerical aperture of 1.2 or moreamong the light beam proceeding from the solid immersion lens 26 to theoptical storage medium 18, does not transmit through the air gap, but istotally reflected in the near field generating portion or in the insideof the air gap. As can be seen from FIG. 5 showing a reflectance withrespect to the numerical aperture of 1.5, the air gap reflective lightNB has a relatively higher reflectance. Also, since the air gap and therecording layer are very close to each other, an interference occursbetween the air gap reflective light (NB) and the recording layerreflective light (RB). Finally, the air gap reflective light (NB)functions as noise with respect to the recording layer reflective light(RB).

[0015] Now, the problem caused by the optical storage medium 18 which ismade at high density will be described with reference to FIG. 6. In thecase that the optical storage medium 18 is fabricated into a highdensity optical storage medium, grooves or pits of 100-150 nm width areformed on a substrate 181 for recording information thereon. Areflective layer and a recording layer on which information is actuallyrecorded are in turn put on the grooves or pits, through a coatingprocess. In addition, a protective layer 183 of 150-200 nm thickness isformed on the recording layer. In FIG. 6, an unevenness structure 185formed by forming the grooves or pits on the substrate 181 is shown inthe form of wedges or wells. Since the depth of the recording layercoated by the protective layer 183 is larger than the width of thegrooves or pits, the light beam 1 incident to the optical storage medium18 from the solid immersion optical system 14 or the solid immersionlens 26 does not reach the grooves or pits, or more accurately, therecording layer, but is reflected in the vicinity of the inner side onthe surface of the protective layer 183. As a result, the optical datastorage system cannot perform writing and/or reading of information withrespect to the high density optical storage medium 18.

SUMMARY OF THE INVENTION

[0016] To solve the above problems, it is an object of the presentinvention to provide an optical storage medium including an opticaltransmissive layer having a desired thickness between a solid immersionoptical system or solid immersion lens and a recording layer formed onthe optical storage medium, in such a manner that light reflected froman air gap does not function as noise with respect to light reflectedfrom the recording layer, in order to be used together with an opticalpickup having the solid immersion optical system or solid immersion lensfor writing or reading information.

[0017] It is another object of the present invention to provide anoptical data storage system including an optical pickup for recordinginformation on the optical storage medium or reading informationtherefrom.

[0018] Additional objects and advantages of the invention will be setforth in part in the description which follows and, in part, will beobvious from the description, or may be learned by practice of theinvention.

[0019] To accomplish the above and other objects of the presentinvention, there is provided an optical storage medium for storinginformation thereon, which is used together with an optical pickupemitting a light beam to access the information and having a focusingoptical system, the optical storage medium comprising: a recordinglayer; and a protective layer, wherein the distance between an opticalsurface of the focusing optical system and the recording layer issmaller than the wavelength of light used and the thickness of theprotective layer is larger than the wavelength of the used light.

[0020] To further accomplish the above and other objects of the presentinvention, there is also provided an optical storage medium for storinginformation thereon, which is used together with an optical pickupemitting a light beam to access the information and having a focusingoptical system for generating a near field, the optical storage mediumcomprising: an optical transmissive layer having a thickness larger thanone wavelength of the light beam and first and second surfaces opposingeach other, such that the first surface opposes the focusing opticalsystem; and a recording layer which is formed on the second surface ofthe optical transmissive layer.

[0021] To still further accomplish the above and other objects of thepresent invention, there is also provided an optical data storage systemfor writing and/or reading information with respect to an opticalstorage medium, the optical data storage system comprising: an opticalpickup including a focusing lens generating a near field and emitting alight beam to write and/or read the information; and the optical storagemedium including an optical transmissive layer having a thickness largerthan one wavelength of the light beam and first and second surfacesopposing each other, such that the first surface opposes the focusinglens, and a recording layer which is formed on the second surface of theoptical transmissive layer.

[0022] According to the present invention, there is also provided anoptical data storage system for writing and/or reading information withrespect to an optical storage medium, the optical data storage systemcomprising: first and second optical pickups respectively includingfocusing optical systems generating near fields and emitting light beamsto write and/or read the information; and the optical storage mediumincluding a single optical storage medium including a first opticaltransmissive layer having a first surface opposing the first opticalpickup, a second optical transmissive layer having a first surfaceopposing the second optical pickup, and first and second recordinglayers which are respectively formed on second surfaces of the first andsecond optical transmissive layers opposite the corresponding firstsurfaces, wherein the first and second optical transmissive layers eachhave a thickness larger than one wavelength of the light beams and thedistances between the first surfaces of the first and second opticaltransmissive layers and the respective opposing surfaces of the focusingoptical systems are smaller than the one wavelength of the light beams.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The objects and other advantages of the present invention willbecome more apparent by describing in detail the structures andoperations of the present invention with reference to the accompanyingdrawings, in which:

[0024]FIG. 1 shows an existing optical data storage system including anexisting optical disc and a catadioptric solid immersion lens therefor;

[0025]FIG. 2 shows an existing optical data storage system including anexisting optical disc and a refractive type solid immersion lenstherefor;

[0026]FIG. 3 shows a near field generating portion in the optical datastorage system shown in FIG. 1 or 2;

[0027]FIG. 4 is a view for explaining air gap reflective light andrecording layer reflective light which are generated in the optical datastorage system shown in FIG. 2;

[0028]FIG. 5 is a graphical view showing angle-reflectancecharacteristics according to air gap changes in the optical data storagesystem shown in FIG. 1 or 2;

[0029]FIG. 6 is a view for explaining the case that an unevennessstructure formed on a substrate of an optical storage medium is notdetected by an optical pickup in the optical data storage system shownin FIG. 1 or 2;

[0030]FIG. 7 shows an optical data storage system according to a firstembodiment of the present invention, which is used together with anoptical data storage system including a catadioptric solid immersionlens;

[0031]FIG. 8 shows an optical data storage system according to a secondembodiment of the present invention, which is used together with anoptical data storage system including a transmissive solid immersionlens;

[0032]FIG. 9 is a view for explaining the case that an unevennessstructure formed on the substrate of the optical disc is detected by anoptical pickup in the optical data storage system shown in FIG. 8;

[0033]FIG. 10 shows an optical data storage system according to a thirdembodiment of the present invention;

[0034]FIG. 11 shows a hierarchical structure of the optical discaccording to the first embodiment of the present invention; and

[0035]FIG. 12 is a graphical view showing the change of the relativemovement stiction force with the texturing depth in the optical discshown in FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Preferred embodiments of the present invention will be describedwith reference to the accompanying drawings, in which elements havingthe same reference numerals perform the same functions.

[0037] Referring to FIG. 7, an optical data storage system according toa first embodiment of the present invention includes an optical pickuphaving a light transmission and reception portion 10, a reflectivemirror 12, a catadioptric solid immersion optical system 64, and aslider 66, and an optical storage medium 68. Since some elements shownin FIG. 7 perform the same optical functions as those having the samereference numerals shown in FIG. 1, the detailed description thereofwill be omitted.

[0038] The optical storage medium 68 includes a substrate 681, anoptically transparent protective layer 683, and a recording layerdisposed between the substrate 681 and the protective layer 683, and isgenerally in the form of a disc. In the case of an overwritable opticalstorage medium 68, the recording layer is formed by coating an opticallysensitive material on the surface of the substrate 681. The opticalstorage medium 68 is fabricated in such a manner that the light beamoutput from the catadioptric solid immersion optical system 64 transmitsthrough the protective layer 683 having an optical transmissivecharacteristic and forms a minimized beam spot on the recording layer.Differently from the existing optical storage medium 18 having a thinprotective layer 183, the optical storage medium 68 has the protectivelayer 683 thicker than the wavelength of light used. An air gap existsbetween the protective layer 683 and the solid immersion optical system64. Therefore, the surface of the solid immersion optical system 64positioned toward the reflective mirror 12 has an aspherical surface forforming a minimized beam spot on the recording layer of the opticalstorage medium 68, taking the thickness and refractive index of theprotective layer 683 into consideration.

[0039] Alternatively, the catadioptric solid immersion optical system 64is fabricated in the shape and material similar to those of the solidimmersion optical system 14 of FIG. 1. As described above, the shape isslightly changed considering the thickness of the substrate beinggreater than one wavelength of the used light.

[0040] The light beam 1 proceeding from the reflective mirror 12 to thesolid immersion lens 64 is refracted and reflected in the solidimmersion lens 64 and forms a beam spot in the center of the surfaceopposing the protective layer 683 of the optical storage medium 68, asshown in FIG. 7. The slider 66 aerodynamically raises the solidimmersion lens 64 from the surface of the optical storage medium 68 bythe relative movement between the rotating optical storage medium 68 andthe slider 66, and forms an air bearing between the opposing surfaces ofthe optical storage medium 68 and the slider 66. Here, the interval ofthe air gap existing between the surfaces of the solid immersion lens 64and the protective layer 683 is maintained at less than the wavelengthpossessed by the used light, that is the light beam 1 emitted from thelight transmission and reception portion 10. In the optimal case, if theair gap interval is maintained at less than ¼ wavelength, aninterference phenomenon is reduced to thereby obtain an excellentsignal-to-noise ratio.

[0041] The light beam 1 incident to the optical storage medium 68 passesthrough the optically transparent protective layer 683 and reaches therecording layer. Thus, in the case that the optical storage medium 68substitutes for the high density optical storage medium having groovesor pits of 100-150 nm width and a protective layer 683 of 150-200 nmthickness, the optical storage medium 68 has grooves or pits of 100-150nm width and a recording layer of 150-500 nm thickness (the depth fromthe surface of the optical storage medium 68 positioned toward the airgap to the grooves or pits becomes larger than the width of the groovesor pits). Thus, the optical data storage system shown in FIG. 7 canwrite or read information with respect to the high density opticalstorage medium.

[0042]FIG. 8 shows an optical data storage system according to a secondembodiment of the present invention. The optical data storage systemshown in FIG. 8 includes an objective lens 74, a refractive solidimmersion lens 76 and a slider 78, instead of the solid immersionoptical system 64 and the slider 66 shown in FIG. 7. FIG. 9 is aenlarged view of an optical storage medium 88 and the solid immersionlens 76 shown in FIG. 8.

[0043] The objective lens 74 focuses the light beam 1 incident from areflective mirror 22 on the refractive solid immersion lens 76. In thisembodiment, differently from the above-described optical storage medium68, the optical storage medium 88 includes a substrate 881 having anoptical transmissive characteristic on one surface opposing the solidimmersion lens 76, and a protective layer 883 on the other surfacefacing away from the solid immersion lens 76. Grooves or pits forrecording information are formed on the substrate 881 of the opticalstorage medium 88. An unevenness structure 885 formed by the grooves orpits formed on the optical transmissive substrate 881 is illustrated inthe form of wedges or wells concave toward the substrate 881 in FIG. 9.

[0044] The solid immersion lens 76 forms an optimized beam spot on therecording layer of the optical storage medium 88, in the center of thesurface of the solid immersion lens 76 opposing the optical storagemedium 88, using the light beam 1 incident from the objective lens 74.In this case, the objective lens 74 and the solid immersion lens 76 forma beam spot providing a numerical aperture of at least one on theabove-described surface of the solid immersion lens 76. The slider 78raises the solid immersion lens 76 from the surface of the rotatingoptical storage medium 88 and maintains an interval of the air gapbetween the surfaces of the solid immersion lens 76 and the substrate881 as a distance less than ¼ of the wavelength of the light beam 1emitted from the light transmission and reception portion 20.

[0045] In the case that the interval of the air gap is ¼ or more of thewavelength of the used light, the light beam providing the numericalaperture of one or more is totally reflected from the air gap when thelight beam forming the beam spot on the surface of the solid immersionlens 76 opposing the optical storage medium 88 passes through the airgap. Thus, only the light beam providing the numerical aperture of lessthan one is transferred to the optical storage medium 88. The spot sizeof the light beam reaching the optical storage medium 88 becomesrelatively large. However, when the interval of the air gap becomes lessthan ¼ of the wavelength of the used light, the light beam of thenumerical aperture of one or more is transferred to the optical storagemedium 88, and the size of the beam spot becomes small. Also, since theunevenness structure 885 in which the recording layer is formed is farfrom the air gap as compared with the existing optical storage medium,the recording layer reflective light is protected from the interferencedue to the air gap reflective light. Thus, the optical data storagesystem shown in FIG. 8 can write or read information with respect to theoptical storage medium 88 with an excellent signal-to-noise ratio aswell. In FIG. 9, the solid arrow line denotes “recording layerreflective light” reflected from the recording layer of the opticalstorage medium 88 and the dotted arrow line denotes “air gap reflectivelight” reflected from the surface of the solid immersion lens 76, theair gap and the substrate 881.

[0046]FIG. 10 shows an optical data storage system according to a thirdembodiment of the present invention. The system shown in FIG. 10includes a double-sided optical storage medium 90. The optical storagemedium 90 is fabricated in a manner that substrates 681 of two sheets ofthe optical storage media 68 shown in FIG. 7 are adjacent to each otheror contact each other. Otherwise, the storage medium 90 is fabricated ina manner that protective layers 883 of two sheets of the optical storagemedia 88 shown in FIG. 8 are adjacent to each other or contact eachother, or only a protective layer 883 remains after two sheets of theoptical storage media have been incorporated into one. The FIG. 10system includes a pair of the light transmission and reception portions20, the reflective mirrors 22, the objective lenses 74, the solidimmersion lenses 76 and the sliders 78, for the optical storage medium90. Since the operation of the FIG. 10 system can be appreciated by oneskilled in the art well through the above-described embodiments, thedetailed description thereof will be omitted.

[0047] Since fabrication of the optical data storage system for writingand/or reading information with respect to the optical storage medium 90shown in FIG. 10 using the system shown in FIG. 7 or 8 is also apparentto those who have an ordinary skill in the art, the detailed descriptionthereof will be omitted.

[0048] In the above-described first embodiment, the thickness of theprotective layer 683 may become infinitely thick in principle, but it issufficient that the air gap between the solid immersion optical system64 and the protective layer 683 is smaller than one wavelength of theused light. However, considering the practical thickness and thenumerical aperture determining the size of the light spot, the thicknessof the protective layer 683 may be several micrometers to severalhundred micrometers. As an example, the thickness of the substrate of adigital versatile disc (DVD) is 0.6 mm, that is, 600 μm. It is apparentto be more practical in accordance with the above thickness.

[0049] Also, although the optical axis of the solid immersion opticalsystem 64 or the solid immersion lens 76 is not perpendicular to thesurface of the optical storage medium 68 or 88 but is slanted thereto,if the distance between a portion of the surface of the solid immersionoptical system 64 or the solid immersion lens 76 farthest from thesurface of the optical storage medium 68 or 88 opposing the surfaceportion of the solid immersion lens 76, and the surface of the opticalstorage medium 68 or 88 is within the wavelength of the used light, thelight beam reflected from the inside of the air gap or the inside of theoptical storage medium between the air gap and the recording layer doesnot function as noise with respect to the light beam reflected from therecording layer. In particular, if the size of the light beam focused bythe solid immersion optical system 64 or the solid immersion lens 76maintains 0.1-0.2 mm at the time of passing through the surface of theoptical storage medium 68 or 88, an excellent recording or reproductioncharacteristic can be obtained with respect to the optical storagemedium 68 or 88 having dust or damage on the surface thereof.

[0050]FIG. 11 shows a layered structure of the optical disc whichembodies the optical storage medium 68 shown in FIG. 7. The optical discshown in FIG. 11 is a high density magnetooptical disc having arecording capacity of 20 GByte or more, which includes a substrate 681,and a reflective layer 682, a first dielectric layer 686, a recordinglayer 684, a second dielectric layer 685, a protective layer 683 and alubricant film 687 which are put on the substrate 681 in turn. In fact,the optical storage medium 68 may or may not include the dielectriclayer 685. The substrate 681 is made of glass, polycarbonate, PMMA, oran acrylate resin, and has an unevenness structure of a track pitch of0.3-0.4 μm and a groove depth of 50-800 Å. The reflective layer 682 ismade of one of aluminum (Al), nickel (Ni), copper (Cu), platinum (Pt),silver (Ag) and gold (Au), and has a thickness of 500-2000 Å. The firstand second dielectric layers 686 and 685 are made of Si₃N₄, ZnS—SiO₂,etc. The first dielectric layer 686 has a thickness of 100-400 Å and thesecond dielectric layer 685 has a thickness of 300-800 Å. The recordinglayer 684 is made of TbFeCo, NdTbFeCo, TbFe, etc., in order to perform amagnetooptical recording, and has a thickness of 150-400 Å. Theprotective layer 683 can be made of either an optically transparentinorganic material or an organic material. In this embodiment, theprotective layer 683 is made by spin-coating acrylate resin, and has athickness of 5-100 μm. The surface of the protective layer 683 istexturing-processed in order to reduce a stiction called a staticfriction. The interval of a bump by the texturing process is 20-60 μmand a texturing depth (or bump height) is 5-50 Å. The lubricant film 687formed on the protective layer 686 has a thickness of 1-3 nm and is alubricant which does not react chemically with the protective layer 683and is made of PFPE (PerfluoroPolyether). Fomblin Z Dol or Fomblin 2001which is used in a hard disc is used as a lubricant. Galden SV is usedas a solvent mixed with the lubricant.

[0051] Referring to FIG. 12, in the case that texturing is not processedon the surface of the optical disc, a stiction occurs. However, in thecase that texturing having a depth of 5 Å or more is performed, thestiction is reduced.

[0052] In the present invention, the solid immersion optical system orsolid immersion lens has been used. However, it is apparent to thosehaving an ordinary skill in the art that a general focusing opticalsystem may be used instead of the solid immersion optical system orsolid immersion lens, if the air gap between the emergence surface ofthe optical system and the protective layer of the optical storagemedium is smaller than one wavelength of the used light and thethickness of the protective layer is thicker than the wavelength of theused light.

[0053] In the above-described embodiments, the reflective mirror 12 or22 plays a role of transferring the light beam emitted from the lighttransmission and reception portion to the solid immersion lens andtransferring the light beam incident from the solid immersion lens tothe light transmission and reception portion. Thus, various opticalelements which can change an optical path, such as a prism, can be usedinstead of the reflective mirror.

[0054] As described above, the optical data storage system according tothe present invention uses an optical storage medium in which athickness of an optical transmissive layer thereof put between theemitting surface of a focusing optical system such as a solid immersionoptical system or solid immersion lens and a recording layer is largerthan the wavelength of light used. Thus, in the present invention, thelight beam reflected from the inside of the air gap or the inside of theoptical storage medium between the air gap and the recording layer doesnot function as noise with respect to the light beam reflected from therecording layer. Also, in the present invention, since the thickness ofthe protective layer or the substrate which becomes the external surfaceof the optical storage medium is increased, information can be writtenor read accurately with respect to the optical storage medium havingdust or damage.

[0055] Although a few preferred embodiments of the present inventionhave been shown and described, it would be appreciated by those skilledin the art that changes may be made in this embodiment without departingfrom the principles and spirit of the invention, the scope of which isdefined in the claims and their equivalents.

What is claimed is:
 1. An optical data storage system for writing and/orreading information with respect to an optical storage medium, theoptical data storage system comprising: first and second optical pickupsrespectively including focusing optical systems generating near fieldsand emitting light beams to write and/or read the information; and theoptical storage medium including a single optical storage mediumincluding a first optical transmissive layer having a first surfaceopposing said first optical pickup, a second optical transmissive layerhaving a first surface opposing said second optical pickup, and firstand second recording layers which are respectively positioned in secondsurfaces of said first and second optical transmissive layers which areopposite the corresponding first surfaces, wherein said first and secondoptical transmissive layers each have a thickness larger than onewavelength of the light beams and the distances between the firstsurfaces of said first and second optical transmissive layers andrespective opposing surfaces of the focusing optical systems are smallerthan the one wavelength of the light beams.
 2. The optical data storagesystem according to claim 1, wherein each of said first and secondoptical transmissive layers is a protective layer.
 3. The optical datastorage system according to claim 2, wherein each of said first andsecond recording layers is formed of a plurality of grooves or pits,wherein said grooves or pits each have a width which is less than athickness of said corresponding protective layer from the first surfaceto the grooves or pits.
 4. The optical data storage system according toclaim 1, wherein each of said first and second optical transmissivelayers is a substrate having an unevenness structure formed on thesecond surface thereof, wherein the unevenness structure forms apre-formatted structure for storing the information.